I think when we say that chess is a conversation, we are using a synecdoche (Ron used that word ages ago to mean a cargo-cult or fetishistic conflation of a specific thing with a general rule, but I'm using it backwards, as a thing that totally is both a class and a prototype of that class.):

RPGs are D&D, interactive communication is conversation. But sometimes what was the beginning of a field is not actually representative over time, as things diverge and find a new centre of gravity, not in terms of prevalence, but in terms of the connections between explored possibilities. It becomes possible to say that new things are uniquely "rpgs" more so than D&D is.

Or in the case of conversation, you have Derrida's criticism of emphasising speech, and referring to other kinds of acts as derivative of it. He emphasises the idea of the text, which is so prone to misunderstandings that to twist it away from the author is to express it's primary nature. Lots of media theory came to rely on precisely this, shifting communication from using face to face conversation as it's model to using the mercurial text, with it's allusions and linkages and conflicting definitions.

What this looses is interactivity, and now we get the conversations online, that combine both of these, the author is still present, but the text speaks for itself too, as people take things out of context, interpret things in terms of other events that have no relation to the authors intent.

A rambling twitter feud or chaotic forum thread synthesises the ideas of the "conversation" as interpersonal interplay, and "text" as tangled reference machine, and creates a new synecdoche; conversation is about the conditional complicated chemical reactions of meaning.

What becomes an edge case in that class is the old "logos", of an idea clearly stated, of a rhetorical argument pulled through to completion based on your capacity to react to your audience's reception of your ideas. Wrestling control of meaning by using the interactions at your disposal is totally alien to this model, it seems far too demanding. Despite being core to another definition of what it means to have communicated something.

To put that more simply, in the self-challenging world of the internet, a "lecture" in the sense of pushing a specific argument, is sort of the opposite of a conversation, or at least an edge case.

You can sort of think about RPGs in that way too; they get momentum from being a conversation in the rambling internet sense; the tension you were talking about ages ago can come from people not quite being able to head where they were originally going, because the game keeps tagging parts of what they said with extra connotations they weren't necessarily expecting:

Moves trigger, moves snowball. /That might not be so easy, draw a card.

The capacity to interrupt and insert new assumptions that weren't meant to be "active" in what someone was going for tied to the means they were using as if they had a life of their own (you want to say something, but you have to use words, you want to get your opponent's king, but you have to get the pieces over to him) can transform the nature of the original task.

Talking about something with someone can be more valuable if they misunderstand you than if they just agree, because you have to revisit the topic in greater detail, investigate it's mechanics.

But an RPG that just resolved into semantics, contradicting dice rolls and complication, would be like a chess game that no-one ever won. You need a bit of that logos thing going on too, so that people can express an idea and know that they have expressed it. Get the feedback coming back that their thing has landed.

In that other model of rpgs as conversation, an rpg is about facilitating mutual understanding of creative ideas, clearing out the confusions of a few people talking about something imaginary, and helping them to know they understand each other.

There's also a strand of rpgs as short term aural history too, which probably relates to this idea of being "heard" and being able to get a reflection of your own ideas back at you, in the sense that aural history requires you to be able to bounce an idea back and forth between people without it changing much, so that it can actually be stored independent of a single persons memory.